1. Field of the Invention
The object of the present invention is a process for the production of microspheres of thorium, uranium, and plutonium oxides, and their mixtures, containing carbon, prepared through the addition to the starting solution, of a polymerizing organic substance, under alkaline conditions.
Microspheres of thorium, uranium or plutonium oxides and their mixtures containing carbon are used either as fuel for high temperature gas cooled nuclear reactors, or for the preparation of carbide microspheres which in turn are used in reactors of the type mentioned or of a different type.
In the first case, the microspheres of thorium, uranium and plutonium oxides containing carbon are used. In the second case, the microspheres are subjected to thermal treatment to cause carburization of the oxides.
In both cases, it is desirable that the carbon is distributed in the most homogeneous way possible and that the microspheres have good compactness and solidity.
2. Prior Art
By making use of the production method of microspheres indicated in the Italian patents of Snamprogetti S.p.A. No. 727.301 and No. 778.786, microspheres of thorium, uranium and plutonium oxides containing carbon may be obtained by adding finely divided carbon to the starting solution. For example, the method described in the Italian patents mentioned may be used by dispersing finely divided carbon (carbon black) in the solutions of the uranium salts (for example uranyl nitrate) and of thorium and of plutonium together with a polymer soluble in H.sub.2 O, by dripping said solutions in aqueous ammonia.
After an aging of the microspheres thus obtained in a solution of ammonium hydrate for about 2 hours, the microspheres are subjected to a fast washing with water to remove the foreign ions, for example the NH.sub.4 + and the NO.sub.3.sup.-, and then dried.
The dried microspheres are subsequently subjected to a thermal treatment at high temperature.
Since the microspheres thus obtained, depending upon the content of carbon, may present soft, brittle or a low abrasion resistance, in Italian patent Nr. 933.615 of Agip Nucleare S.p.A., a method for impregnating microspheres obtained as above-mentioned to give them a suitable solidity and compactness was claimed subsequently.